It's possible that you've encountered a threat Norton isn't yet aware of, given the sheer volume of new threats that are generated every day, many of which are unique, extraordinary threats that are designed to seriously damage your particular system. Similarly, some malware specifically designs its programming to render its adversary inoperable. Because they don't have clean code that can be fixed, Trojans and worms can be very difficult to remove; instead, they need to be physically removed.
